United States Department of Agriculture data indicates that world oilseed production reached a record 307.8 million metric tons in 2000. Soybeans represented more than half (56%) of all oilseeds grown throughout the world, followed by rapeseed (12%), cottonseed (11%), peanut (10%), sunflower (7%), palm kernel (2%), and copra (2%). Most of this oilseed crop was processed into edible vegetable oils and protein-rich oilseed meals. Oilseed-derived edible oils were the major source of the 87.2 million metric tons of vegetable oils consumed worldwide in 2000. Oilseed-derived protein meals provided more than 90 percent of the 173.9 million metric tons of the protein meal consumed worldwide in the same period.
The United States 2000 oilseed crop chiefly comprised soybeans, cottonseed, sunflowers, and peanuts. Soybeans dominated, representing 85 percent of all oilseeds grown domestically. Cottonseed ranked a distant second at 8.7 percent, with the remaining percentage share split in a 7:6 ratio between sunflowers and peanuts. For soybeans alone, United States growers devoted a crop area of 74.5 million acres (30.2 million hectares), producing 2.77 billion bushels (75.39 metric tons) of soybeans for a total crop value of $12.2 billion. Much of this soybean crop underwent processing, yielding 17.9 million metric tons of refined soybean oil and 38.2 million metric tons of soybean meal.
Refined vegetable oils are primarily utilized in food products such as shortening, margarine, cooking and salad oils, and confectionary fats. Lecithin, obtained as a valuable byproduct of the vegetable oil refining process, is used in a wide variety of applications ranging from pharmaceuticals to protective coatings. After removal of the oilseed oils, the resulting high-protein oilseed meals are widely used as animal feeds. To a lesser extent, oilseed meals and/or protein products derived therefrom are used in certain human foods.
Oilseed chemical composition varies based on type of oilseed, plant variety, cultivation history, and climactic conditions. Oilseeds are composed primarily of seed coat (hull), oil, protein, water, mono- and oligo-saccharides (also termed sugars), and other minor constituents. Soybeans in particular typically comprise about 20–22 percent by weight oil, about 42–46 percent by weight protein, and about 35 percent by weight carbohydrates on a moisture-free basis.
Several minor oilseed components, such as free fatty acids and coloring matter, can impart objectionable properties to oilseed byproducts and hence must be removed during processing. Other minor oilseed components, such as phosphatides (also termed lecithin), sterols, tocopherols, and isoflavones, can be valuable when isolated and recovered.
Soybeans differ from the other major oilseeds in several respects. Soybeans have a relatively low seed coat (also termed hull) content compared to other oilseeds, and hence are lower in crude fiber. Although soybeans are generally lower in oil content, their protein content far surpasses other oilseeds. Soybeans also uniquely contain several beneficial members of the isoflavone chemical family.
Isoflavones are natural flavonoids that exhibit estrogenic activity. Natural isoflavones are sometimes referred to as phytoestrogens (plant-derived estrogens). The generic chemical structure of isoflavones is given by formula 1 below.
1 R1R2R3(1a) GenisteinOHHOH(1b) DaidzeinHHOH(1c) GlyceteinHOCH3OH(1d) GenistenOHHO-glucose(1e) DaidzinHHO-glucose(1f) GlycetinHOCH3O-glucose
Soybean isoflavones comprise the aglycone forms genistein (1a) (5,7-Dihydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one; 4′,5,7-trihydroxyisoflavone) [CAS No. 446-72-0], daidzein (1b) (7-Hydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one; 4′,7-dihydroxy-isoflavone) [CAS No. 486-66-8], and glycetein (1c) (6-Methoxy-7-hydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one), as well as the glycoside forms genisten (1d), [CAS No. 529-59-9], daidzin (1e) and glycetin (1f). Soybean isoflavones exist in the plant mainly in the glycoside forms genisten (1d), daidzin (1e), and glycetin (1f). Total soybean isflavone concentration is about 0.1–0.4 weight percent on a dry basis. The concentration of individual isoflavones present in soybeans is about 0.033–0.2 weight percent genistin, about 0.015–0.08 weight percent daidzin, about 0.005–0.01 weight percent glycetin, and about 0.01–0.04 weight percent of daidzen, genistein, and glycetein. Wang, H., and Murphy, P. A., Isoflavone Composition of American and Japanese Soybeans in Iowa: Effects of Variety, Crop Year, and Location. Journal of Agricultural and Food Chem. 1994, 42, 1674–1677.
Epidemiological studies indicate that diets rich in isoflavones lead to a lower incidence of breast and prostate cancer. Isoflavones also appear to reduce heart disease, gallbladder disease, osteoporosis, menopausal difficulties, and lung, colon, stomach, and uterine cancers. The molecular structure of isoflavones is similar to that of the principal human estrogen 17-β-estradiol [CAS No. 50-82-2], compared to which soybean isoflavones demonstrate about 2 percent estrogenic activity.
The main mechanism of action of isoflavones appears to be their ability to bind to the same cellular estrogen receptor (ER) sites as do estrogens. Upon binding, isoflavones display activity as selective estrogen receptor modulators (SERM), meaning that they exert estrogenic action at sites where such action is believed to be favorable, such as the bones and heart, but have no effect or even an antiestrogenic, i.e. inhibitory, effect at sites such as in the uterus and breast where estrogenic action is undesirable. Thus for example, isoflavones can modulate certain cell receptors to reduce bone loss and at the same time preempt estrogen from occupying breast tumor cell receptor sites at which estrogen might stimulate unwanted growth.
In a second mode of action, isoflavones may also indirectly reduce endogenous estrogen production. Gonadotrophins released by the pituitary gland stimulate estrogen synthesis in the ovaries. Isoflavones appear to lower gonadotrophin levels, thereby lengthening menstrual cycles. Women having longer menstrual cycles tend not to develop breast cancer. Lowering gonadotrophin levels also tends to reduce unpleasant menopausal side effects such as hot flashes.
Less favorably, soybeans possess relatively high levels of the indigestible oligosaccharides raffinose and stachyose, which has tended to limit their use in human foods. Sucrose (2), raffinose (3), and stachyose (4) are the principal soluble sugars present in soybeans, and occur in a combined amount of about 15–18 weight percent on a dry basis.

Sucrose (2) is a disaccharide composed of one α-D-glucose unit in pyranose form coupled via a glucoside linkage to one α-D-fructose unit in furanose form. Most animals, including humans, possess the enzyme α-glucosidase, which catalyzes hydrolysis of glucoside linkages and enables breakdown of sucrose into simple sugars that can be digested.
Raffinose (3) is a trisaccharide composed of sucrose coupled via a galactoside linkage to an α-D-galactose unit. Stachyose (4) is a tetrasaccharide composed of raffinose coupled via a galactoside linkage to an additional α-D-galactose unit. Because most animals lack the enzyme α-galactosidase, they cannot break down raffinose and stachyose into simple sugars for digestion. Consequently, raffinose and stachyose pass from the stomach to the lower intestinal tract, where they are fermented by microflora to produce flatus, composed mainly of carbon dioxide, methane, and hydrogen. The resulting flatulence typically produces discomfort, diarrhea, lost appetite, poor growth, and in the case of young animals can even result in death. These effects are responsible in part for the lack of widespread use of soybean-derived nutrients in human foods.
In recovering oil from oilseeds, most processors employ solvent extraction. An optional pre-extraction mechanical pressing step is sometimes used when processing high-oil oilseeds such as sunflower and peanut to remove an initial fraction of oil and thereby reduce the amount of solvent that must be recovered from the extracted oil. Mechanical pressing, also termed expelling, generally involves screw-pressing oilseeds at low pressure to produce an extracted oil fraction and a press cake containing about 5 percent residual oil. Oil obtained from mechanical pressing is similar to that obtained from solvent extraction, but typically contains less phosphatides.
Typical solvent extraction processes involve the four basic steps of preparation, extraction, solvent recovery from the extracted oil (termed miscella), and desolventizing/toasting or flash desolventizing of the de-oiled seed meal. Conventional preparation generally comprises the steps of (1) rough cleaning (often termed scalping) to remove foreign material; (2) drying to loosen hulls; (3) additional cleaning; (4) cracking to break the oilseed into pieces properly sized for dehulling and flaking; (5) optional dehulling (if seeking to produce high-protein meal for animal consumption or flour for human consumption); (6) conditioning to adjust temperature to approximately 70° C. (160° F.) and water content to less than about 11 percent by weight; (7) flaking; and (8) optionally converting flakes into collets via use of “expanders.” Flake thickness generally ranges from about 0.2 mm (0.008 in) to about 0.5 mm (0.02 in). In the optional colleting step, expanders (also termed extruders) are used to transform flakes into sponge-like extrudates termed collets. Collets are larger, denser, less fragile, and more porous than flakes. Thus, collets are not as likely as flakes to hinder solvent percolation, and hence extract more rapidly and drain more completely after extraction, thereby reducing the amount of solvent that must be recovered in desolventizing of the extracted solids.
In conventional solvent extraction, solvent partitions oil, phosphatides, and other solvent-miscible components into a liquid miscella phase, leaving a de-oiled seed meal (also termed extracted drained flakes or extracted solids). Physical contact between the solvent and prepared oilseeds typically occurs either by immersing prepared oilseeds in solvent, percolating solvent through a bed of prepared oilseeds, or some combination of both. Solvent in the miscella phase is recovered by vaporization, generally conducted under steam stripping conditions. Residual solvent in the de-oiled seed meal, sometimes referred to as hold-up solvent, is generally recovered either in a desolventizing/toasting system or in a flash desolventizing system, depending on the intended use of the meal. If a lecithinated meal is desired, phosphatides must be added back to the de-oiled seed meal in an extra processing step.
Desolventizing/toasting systems are used to produce a toasted product that is nutritionally well suited for use in animal feeds. The term “toasted” as used by oilseed processors generally means cooked with steam, rather than dry heat. Desolventizing/toasting generally comprises removing solvent and then cooking at 100–105° C. (221–220° F.) at moisture levels ranging from 16 to 24 percent for a time of from about 15 to about 30 minutes. In a typical desolventizer/toaster, steam injected into the de-oiled seed meal furnishes heat required to vaporize the solvent, inactivates antinutritional factors such as trypsin inhibitors and lectin, and elevates moisture levels to facilitate toasting.
Flash desolventizing systems on the other hand are used to produce human foods such as flours, protein concentrates, or protein isolates. Extracted flakes used as precursors in such food production must be desolventized with minimal heat exposure in order to preserve high protein content. In a typical flash desolventizing system, superheated solvent vapor is injected into and conveys the extracted drained flakes to a desolventizing tube, within which the hold-up solvent rapidly vaporizes within about 2 to 5 seconds. The product generated by flash desolventizing is often termed “white flakes.”
Desolventized/toasted flakes normally undergo grinding to meet a desired particle size range and are then sold as oilseed meal, chiefly for incorporation into livestock feeds as a principal source of protein. However, typical oilseed meals contain from about 9 to about 15 percent by weight flatulence-promoting indigestable oligosaccharides, including raffinose and stachyose, which limits their use to a certain extent in livestock feed formulations. In an extra processing step, such indigestable oligosaccharides can be extracted with ethanol. Alternatively, the relatively expensive α-galactosidase enzyme is sometimes added to the diet to address the issue of undesirable oligosaccharide content.
Certain oilseed meals must meet standards established by the National Oilseed Products Association (NOPA). For example, NOPA rules provide that non-dehulled soybean meal, often termed low-protein or low-pro meal, must contain at least 44 percent by weight protein and less than 7 percent by weight fiber. Dehulled soybean meal, often termed high-protein or high-pro meal, is required by NOPA to contain at least 48 percent by weight protein and less than about 3.75 percent by weight fiber. Low-protein soybean meal is an excellent protein source for mature livestock and poultry, and is especially ideal for high-energy rations such as broiler, turkey, and pig starter feeds. High-protein meal is preferred in feeding young animals and birds.
Flash-desolventized white flakes are either ground and sold as grits or flour, or are processed further to generate protein concentrates or protein isolates. In a tentative final regulation issued Jul. 14, 1978, (43 Fed. Reg. 30472, 30489) the Food and Drug Administration (FDA) proposed the following definitions for vegetable protein products. A product containing less than 65 percent by weight protein on a moisture-free basis is termed “------ flour,” the blank to be filled in with the name of the protein source. A product containing 65 percent or more but less than 90 percent by weight protein on a moisture-free basis is termed “------ protein concentrate,” the blank to be filled in with the name of the protein source. A product containing 90 percent by weight or more protein on a moisture-free basis is termed “------ protein isolate,” the blank to be filled in with the name of the protein source.
The nutritional qualities of protein meals or flours and their derived products are determined primarily by protein content and amino acid composition. The World Health Organization (WHO) recommends that protein products be required to contain a minimum content of certain essential amino acids, as shown in Table 2.
TABLE 2FAO/WHO/UNU-RecommendedEssential Amino Acids Requirements (mg/g protein)Amino AcidChild, age 2–5Child, age 10–12AdultLysine584416Methionine252217CystineThreonine34289Histidine191916Leucine664419Isoleucine282813Valine352513Phenylalanine632219TyrosineTryptophan1195
Protein meal composition depends not only on oilseed type and but also on processing conditions. For example, overheating tends to destroy key amino acids, such as methione, lysine, and cystine.
Grinding of flakes to form flour or grits typically occurs via hammer mills, pin mills, or classifier mills. Particle size requirements for protein flours generally provide that at least about 97 percent must pass through a U.S. Standard No. 10 Sieve. Grits are generally less fine than flour, and are milled to meet a wide variety of manufacturer- and/or buyer-specified particle size ranges. Soy flour and grits are used in the commercial baking industry as dough conditioning and bleaching aids. Their moisture-retaining qualities also help retard staling.
Protein concentrates are produced by subjecting protein flours to an additional processing step, typically comprising extraction with alcohol, to remove certain components, including objectionable flavor compounds and oligosaccharides. Further additional processing of protein concentrates yields protein isolates, which typically are produced by three main procedures: aqueous-alcohol extraction, acid leaching, and protein denaturing. Processors have long sought simpler methods for producing protein concentrates and protein isolates that employ fewer steps.
Conventional methods for producing soybean protein concentrates generate a sludge, often termed chromasoy molasses, into which isoflavones have been carried throughout processing. Isolating and recovering isoflavones from such sludge is a complicated, lengthy, and expensive process. Thus, soybean processors have long searched for better methods for recovering isoflavones.
Most oilseed solvent extraction operations utilize a solvent blend termed “hexane,” which is not pure n-hexane but rather is a mixture of C6 saturated aliphatic and alicyclic hydrocarbons, principally comprising n-hexane, isohexane, and methylcyclopentane, whose boiling points fall within a narrow prescribed range. Extraction-quality hexane is flammable, however, and fluctuates widely in price based on petroleum supply fluctuations. Hexane also is not a GRAS (Generally recognized As Safe) substance, and must be removed from products intended for human consumption. Hexane recovery from miscella and extracted drained flakes is energy-intensive, and the use of hexane is heavily restricted or even banned in certain countries based on environmental concerns. Moreover, hexane-extracted crude oil is a dark-colored, turbid liquid having unacceptable odor and flavor, and which requires substantial further treatment to convert it into a bland, stable, and nutritious product. Such further treatment usually consists of a number of steps collectively referred to as the refining process, which are necessary to remove components such as phosphatides, free fatty acids, sterols, tocopherols, and coloring matter. The refining process typically includes several time-consuming and expensive steps such as degumming, introducing chelating agents to remove trace metal compounds, neutralizing/deacidifying, bleaching, and deodorizing. The capital cost associated with equipment to practice these refining steps is quite high, and traditional refining processes inherently generate oil losses because each refining step produces a residue containing a certain amount of otherwise usable oil, thus decreasing the final yield of oil. Accordingly, oilseed processors have long searched for alternatives to hexane extraction.
Numerous oilseed extraction methods that do not employ hexane have been proposed. Many hexane alternatives have been investigated, including aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, trichloroethylene, and dichloroethane; alcohols; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether; and esters such as ethyl acetate. For example, Eaves, P. H. et al., JAOCS 29:88 (1952), compared hexane to four alternative solvents (benzene, ethyl ether, acetone, and butanone) in extracting cottonseed flakes. The more polar solvents acetone and butanone yielded crude oils higher in non-oil content compared to hexane-extracted crude oil. After refining and bleaching, none of the non-hexane-extracted oils were as light in color as hexane-extracted oil. The study concluded that none of the alternative solvents compared favorably to hexane.
Halogenated hydrocarbons such as methylene chloride are nonflammable and thus have a distinct advantage over hexane. However, even though extraction studies indicate that methylene chloride compares favorably to hexane, the FDA has delisted many chlorinated solvents because of toxicity concerns.
Alcohols such as ethyl alcohol and isopropyl alcohol have been extensively studied as hexane alternatives in solvent extraction. For example, U.S. Pat. Nos. 4,144,229 and 4,219,470 disclose a four-step process for extracting oilseeds comprising sequentially contacting oilseeds with increasingly concentrated ethanol solutions. Isopropanol extraction is described in U.S. Pat. No. 4,298,540 and in a study by Harris et al., published in three parts at JAOCS 24:370–375 (1947), JAOCS 26:719–723 (1949), and JAOCS 27:273–275 (1950). However, unlike hexane-oil miscellas, mixtures of oil and alcohol are not completely miscible at all ratios. Also, maximum solubility of oil in alcohol can only be achieved by using absolute alcohol grades, which are expensive and difficult to obtain without special distillation methods to overcome azeotrope formation. Moreover, alcohols present flammability concerns. Furthermore, because the latent heat of vaporization of many alcohols is substantially higher than that of hexane, recovery of alcohols via conventional distillation practices is not energy efficient, and requires expensive equipment modifications.
Certain aqueous extraction processes also are known, as noted by Lusas et al., in an article entitled Separation of Fats and Oils By Solvent Extraction: Non-Traditional Methods, contained in World Conference Proceedings, Edible Fats and Oil Processing, Basic Principles and Modern Practices, American Oil Chemist's Society 1989:56–78. However, as acknowledged by Lusas et al., the primary interest of prior aqueous extraction processes is preserving the nutritional properties of protein in the extracted miscella, and the extracted oil itself has only secondary interest. Moreover, extraction with water alone, even when the water is heated to near boiling, leaves behind significant quantities of oil. Thus, a chief limitation of prior aqueous extraction processes is that the extracted miscella and protein products derived therefrom contain relatively large levels of residual oil.
Solvent mixtures also have been investigated. For example, King et al., JAOCS 38:19 (1961) extracted gossypol from cottonseed flakes using a 44:53:3 acetone:hexane:water mixture. However, crude oils obtained with that solvent mixture contained more impurities than oils extracted with hexane. Moreover, desolventizing an oil-solvent miscella containing mixed solvents and then reclaiming the individual solvents from the recovered solvent mixture both can be quite complex operations.
Thus, previously known methods for treating oil bearing vegetable material all suffer from particular advantages, and processors continue to seek further improvements.